The invention relates to the technical field of the control of multiphase electric motors for automobile vehicles.
The traction machines of electric vehicles are electrically powered by transistor systems designed to generate single-phase alternating voltages from a DC voltage. This power electronic system is called a voltage inverter. The control of the switches included in the voltage inverter is carried out by signals modulated in pulse width (PWM for pulse-width modulation). Pulse-width modulation consists in generating a train of pulses at a fixed frequency and with variable width, whose average value corresponds to the value of the setpoint applied.
Various methods exist that are conventionally used to obtain such a modulation.
The sinusoidal method allows a PWM modulation with a zero or very low voltage to be supplied.
The injection of a third-order harmonic allows the amplitude of the main harmonic to be increased. This method has been developed principally for increasing the linear voltage region. It does however have the drawback of increasing the rms value of the current and hence the losses, both in the power electronics and in the motor.
Space Vector Modulation has been developed in order to increase the linear voltage region, while at the same time avoiding the increase in current caused by the harmonic injection.
Discontinuous methods allow the switching losses to be minimized in the transistors while at the same time conserving a good use of the voltage available and a limitation of the current. Their main drawback is being difficult to implement and not easily compatible with the real duty cycle limits. The reason for this is that, owing to the dispersion in switching times of the transistors, a voltage inverter must comprise a dead time in order to limit the duty cycle values.
The document US 2009/0179608 describes a method for controlling a voltage inverter supplying power to an electric motor of an automobile vehicle. The method described takes into account constraints on forbidden regions of the duty cycles in the case of a chopping frequency that can be variable. This method is of the space vector modulation type.